In general, in tribology, the characteristics of fluids are of notable practical concern and a cause for much study. In the automotive industry especially, it is important to be able to determine and predict the viscosity and performance characteristics of an engine oil or other lubricants without having to test the same in an actual engine or other working mechanism. Further as well, in the printing industry, the characteristics of printing inks can be of critical concern.
Several rotational viscometers have been developed, which are intended, among other things, for studying such non-Newtonian fluids as multigrade motor oils formulated by blending viscosity index improvers, synthetic polymers, and so forth, into straight mineral oils. See, Kim et al., U.S. Pat. No. 3,350,922 (Nov. 7, 1967), and W. C. Pike et al., "A Simple High Shear Viscometer," SAE Publication No. 780981 (1978). Generally, such instruments, although useful, are complex, expensive, sometimes unstable, and reliable only in the hands of qualified scientists.
In ameliorating or overcoming such problems as these, Theodore W. Selby invented and disclosed a tapered bearing simulator-viscometer, U.S. Pat. No. 4,445,365 (May 1, 1984). It is characterized by simple, benchtop operation, and its commercial embodiments, available from Tannas Co., Midland, Michigan, U.S.A., are believed to be the only very high shear (100,000 per reciprocal second and beyond) absolute viscometers commercially available--shown in ASTM studies to be the most accurate and precise of known very high shear rate viscometers, thus being suitable for production control as well as an excellent research tool. Organic and water based liquids, including engine oils, automatic transmission fluids, hydraulic fluids, waxes, and polymeric solutions have been tested on the tapered bearing simulator-viscometer at viscosities ranging from 1 to 100 centipoise (cP) depending on the temperature and shear rate. See, e.g., Tannas Co., catalog, pages 2 & 3 (1994).
Be that as it may, even the highly successful tapered bearing simulator-viscometer of Mr. Selby has its drawbacks. Chief among these are the following:
1) A hystersis synchronous motor is used, in which rotational speed is proportional to the frequency of the alternating current electrical input. For example, with an alternating current of 60 cycles per second, the motor speed is 3600 rotations per minute (rpm). However, if electrical devices, as for example, a refrigeration compressor, are operated on the same circuit, a change in the the number of cycles per second of the alternating current may occur. This in turn causes the motor speed to fluctuate, which in turn causes torque to fluctuate, which causes the instrument readout related to viscosity to fluctuate inaccurately.
2) The motor is housed in a motor housing which is supported on a turntable assembly in a platform and which rotates within a limited arc; supporting the turntable are eight ball bearings in a circular race. The bearings in this arrangement can drift and/or get dirty, causing the turntable/housing to lean, which in its turn also causes the instrument readout related to viscosity to shift inaccurately.
3) The motor is fed electricity through lead wires. The lead wires, which are external to the motor housing, and may dangle, can tug or pull, thus creating unpredictable drag not related to fluid viscosity, which in turn causes the torque values to shift, which causes the instrument readout related to viscosity to shift inaccurately.
4) The motor, rotor and stator assembly is supported on the platform, which is cantilevered from a slide plate as its only support. This arrangement can cause slight alignment problems, which in turn causes the torque and so forth to shift, which causes the instrument readout of viscosity to fluctuate inaccurately.
Although the inaccuracies caused by such arrangements of the Selby tapered bearing simulator-viscometer can be small, greater and greater accuracy and precision is being demanded in the viscometry art. See, e.g., Hydrock, "Automotive Lubricant Test Standards Keep Tightening," Lubricants World, Vol. 4, No. 12, pages 7, 10-11 & 14 (Dec. 1994).
It is desirable, accordingly, to overcome such problems, and be able to provide even more accurate and precise ways and means to measure fluid viscosity.